Sensitivity to Oxygen of Nitrogenase Activity in Rhizobium Strain ANU289 of the Non-legume Parasponia (Ulmaceae)

Abstract

Nitrogenase activity can be detected in Rhizobium strain ANU289 of Parasponia in shaken liquid cultures. A combination of consistently low oxygen tension and appropriate cell density was found to be essential for rapid initiation and high specific rates (in the range of 50-60 nmoles of ethylene per milligram protein per hour). In the presence of succinate as carbon source and an oxygen concentration of 0·25% (v/v) in the gas phase, nitrogenase activity developed after incubation for 24 h. The requirement for an oxygen concentration in the range of O· 1 to 0·35% for derepression indicated a lack of any inherent tolerance to higher oxygen levels and thus suggests that plant-derived mechanisms are responsible for protection by oxygen in the nodule.